The great fish migration has begun

Rising sea temperatures are pushing shoals of fish hundreds of kilometers from their native grounds, with warm-water fish now landing in northern nets

By Robin McKie / The Guardian

Illustration: Mountain People

Scottish fishermen have uncovered an intriguing way to supplement their income: They have added squid to the menu of marine creatures they regularly pull from the sea. A species normally associated with the warmth of the Mediterranean Sea, rather than the freezing north, might seem an odd addition to their usual catches of cod and haddock. Nevertheless, squid has become a nice little earner for fishing boats from Aberdeen and the Moray Firth.

Thirty years ago, squid was a rarity in the North Sea. Today, boats bring back thousands of tonnes per year — although cod and haddock still dominate catches. Nor is this warm-water addition to northern fish menus a unique feature. Red mullet, sardines and sea bass have also appeared with increasing frequency in North Sea fishermen’s nets. All of them are associated with warmer waters and their appearance is seen by many scientists as a sign that climate change is beginning to have a serious impact on our planet’s oceans.

For Scottish lovers of fresh squid, this is good news. However, in many other parts of the world, rising sea temperatures — triggered by climate change — are providing fishing industries and governments with major headaches. Fish are moving hundreds of kilometers from their old grounds, sometimes out of zones that had been set up to protect them. In other cases, fish are simply disappearing from nets.

Part of the problem has its roots in past overfishing. However, climate change is now exacerbating the issue. Scientists last week revealed that a vast chunk of ice was set to break away from the Antarctic Larsen C ice shelf, while Arctic sea ice extent is now at its lowest level for this time of year since records began.

In addition, if sea temperatures continue to rise, even greater disruption would be caused to fishing stocks. Fishermen would lose their livelihoods and communities would be deprived of their only source of food.

“There is an unambiguous trend,” Miami University marine biologist Andrew Bakun said. “If you look at the world’s fish catches as a whole, you find they are made up, more and more, of warm-water species as opposed to catches in previous years which had more species that were from cooler waters.”

Seafood is the critical source of protein for more than 2.5 billion people. However, overexploitation has resulted in a crash in fish stocks, with the result that the world’s annual catch is now decreasing by more than 1 million tonnes every year — despite the availability of the latest fishing technology: Nets big enough to engulf cathedrals, echo locators, satellite navigation and powerful engines to drive boats.

Now climate change is making the management of this threatened supply even more difficult.

“All the world’s oceans are facing intense problems, but the problem is going to be particularly serious for tropical countries, which are often underdeveloped and are far less able to maintain sustainable management regimes for their fisheries,” said Callum Roberts, a marine biologist at Britain’s York University.

An example is provided by Bangladesh. Fish gives the nation 60 percent of its animal protein and is vital to the 16 million Bangladeshis living near the coast, a number that has doubled since the 1980s.

However, a study — led by Jose Fernandes of the Plymouth Marine Laboratory — of two key fish species, Hilsa shad and Bombay duck, showed that stocks of both could be devastated by climate change that would affect nutrient flows in coastal waters, ocean temperatures and sea levels.